Zinc oxide semiconductor materials comprising zinc and oxygen as constituent elements have recently attracted considerable attention since they can emit not only blue light but also near ultraviolet rays of 400 nanometers or less because of their wide band gap similarly to semiconductor materials such as gallium nitride and the like. Further, their applications to photodetector, piezoelectric device, transparent conductive electrode, active device and the like have also been expected without being limited to light emitting device.
To form such zinc oxide semiconductor materials, various methods such as MBE method using ultra-high vacuum, sputtering, vacuum evaporation, sol-gel process, MO-CVD method, and the like have been conventionally examined. With respect to the light emitting device, the MBE method using ultra-high vacuum is widely used from the viewpoint of crystallinity. In each of these conventional growth methods, for example, a growth method shown in Appl. Phys. Lett., 41 (1982) 958 by Minami et al., a method using a single-crystalline sapphire substrate reported in Solid-State Physics, vol. 33, No. 1 (1998) by Kawasaki et al., the obtained thin film had c-axial orientation because the energy in crystal growth is the lowest in the c-axial development of the wurtzite structure.
However, not only such a crystal having c-axial orientation is apt to form a polycrystal containing nanocrystals, when the shape is even slightly deformed in the growing stage of crystal, by minimizing the hexagonal shape to arrest the deformation, which makes it difficult to obtain a single crystal film of relatively large area, but also a polycrystal film containing the nanocrystals is apt to cause abnormal properties in electric conduction by the bonding of impurities to the terminal of the nanocrystals or the bonding of a conductive electron to a dangling bond at the top surface, resulting in the deterioration of doping characteristic, luminous light characteristic, and the like.
Accordingly, this invention has been attained from the viewpoint of the above-mentioned problems, and has an object to provide a zinc oxide semiconductor material deterred with respect to the deterioration of doping characteristic, luminous characteristic and the like.